Olympic Monitor

For endurance athletes unwilling to rely on talent and training alone, the booster of choice is the hormone erythropoietin (EPO), which multiplies the red blood cells that carry vital oxygen to tiring muscles. The temptation to use EPO before "any race longer than about four minutes" is powerful, says Dr. Ken Fitch, an Australian member of the International Olympic Committee medical commission. Not only can EPO improve performances by 5-10%, but no test can reliably distinguish between people who've injected the hormone and those whose EPO levels are naturally high. For athletes inclined to cheat, says Fitch, that leaves "one huge loophole."